Hi!
I have a Master-Detail relationship between my custom object and the Opportunity built-in object.

I would like to be able to create a record of my custom object from the Opportunity record via a visualforce page, but i'm not sure how to achieve this.
If I use the standardController as Opportunity, the visualforce page shows up in the page layout builder, but obviously, the code is not working.

Here's the visualforce page:

<apex:page standardController="CFA__c">
    <apex:sectionHeader title="CFA Edit" subtitle="{!CFA__c.Name}"/>
    <apex:form id="CFA_Edit_Form">
        <apex:pageBlock title="CFA Edit" mode="edit">

            <apex:pageBlockButtons >
                <apex:commandButton value="Save" action="{!save}"/>
                <apex:commandButton value="Save & New" action="{!save}" />
                <apex:commandButton value="Cancel" action="{!cancel}"/>
            </apex:pageBlockButtons>


            <apex:pageBlockSection title="Information" columns="2">
                <apex:inputField value="{!CFA__c.Name}" required="true"/>
                <apex:inputField value="{!CFA__c.Type__c}" required="true">
                    <apex:actionSupport event="onchange" reRender="CFA_Edit_Form" />
                </apex:inputField>
                
                <apex:inputField value="{!CFA__c.AE__c}" rendered="{!CFA__c.Type__c == 'Joint Visit'}" />
                <apex:inputField value="{!CFA__c.AE_Description__c}" rendered="{!CFA__c.Type__c == 'Joint Visit'}" />
            </apex:pageBlockSection>

        </apex:pageBlock>
    </apex:form>
</apex:page>

Any way this is achievable with Visualforce?